London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

A letter by Jack Straw asking Tony Blair to consider alternatives to invading Iraq is set to be revealed at the official war inquiry.

The Cabinet heavyweight is said to have written a personal letter setting out other options to taking part in the US-led military action to topple Saddam Hussein.

The existence of a letter hinting that Britain should offer only "political and moral support" has been known about for more than a year but the contents have never been disclosed.

But now a copy is being reportedly passed to the inquiry into the war, headed by Sir John Chilcott, which means Mr Straw is certain to be questioned about his concerns and what motivated him.

Mr Straw, the Justice Secretary, was Foreign Secretary at the time of the invasion in 2003 and is the only senior serving Cabinet minister being called to give evidence before the general election.

His letter was reportedly written after discussions with Sir Michael (now Lord) Jay, the Foreign Office permanent secretary at the time, on 16 March 2003, two days before the Commons voted to back the war.

Some reports claim it urged Mr Blair to cancel Britain's part in the invasion and to inform US President George Bush that UK troops would only help with peacekeeping once the war was over. Others say Mr Straw did not take a strong view but merely set out the alternatives that would see Britain playing a role after the invasion was over.

Mr Blair ultimately decided that British forces should play a full part in the overthrow of the Iraqi dictator. However, if it emerges that his Foreign Secretary advised caution, that would put the spotlight even more firmly on the former Premier as the driving force behind British military participation.

Another key witness next month is Lord Goldsmith, the former Attorney General, who is expected to confirm that he advised that an invasion could be illegal but came under fierce pressure from No 10 to change his mind.

Gordon Brown's own appearance before the Chilcott inquiry has been postponed until after the general election — sparking opposition claims of an establishment "stitch-up" to protect him from controversy.

Mr Straw has never faltered in his belief that the overthrow of the Saddam regime was lawful and justified by the former dictator's defiance of UN resolutions and his attempts to acquire weapons of mass destruction.

However, he is known to have been concerned about the risks of civil war in Iraq after the invasion and to have been uncomfortable with the bellicose tone of the "neo-cons" around Mr Bush.

The Chilcott inquiry team say Mr Straw is being called to give evidence before the election on the grounds that he has since changed ministerial jobs and is no longer responsible for foreign affairs.